[en] RISI is currently conducting research on representative samples of NPP cables both during long-term aging and accident simulation, since insulated electrical cables are used to provide instrumentation signals, power, or control to virtually all remotely operated power plant equipment. The objectives of this program are to determine the suitability of these cables for extended life (beyond 40-year design basis) and to assess various cable condition monitoring techniques for predicting remaining cable life. The cables are being aged for long times at relatively mild exposure conditions with various condition monitoring techniques being employed during the aging process. Following the aging process, the cables are being exposed to a sequential accident profile consisting of high dose rate irradiation followed by simulated design basis loss-of-coolant accident steam exposure. This paper presents some results of a study of NPP cables electrical characteristics at normal and accidental conditions. 6 figs

[en] This report is dedicated to ideology of the computer code, the main purpose of which is the prediction of radiation consequence of fission products release into atmosphere. The principles of mode do not depend on type of reactors. Therefore, it is not necessary to speak about physical characteristics and scenarios of supposed accidents. It is important to have knowledge about range of parameters values, which are important for consequences. 1 fig., 1 tab

[en] The objectives of the Specialist's Meeting were: To provide an international forum for presentation and discussion on experience with instrumentation and equipment for monitoring and controlling NPP post-accident situations; to share experience on the design and improvements in the subject area; to identify and describe advanced features for safety and post-accident management improvements. In order to facilitate a structure discussion and not to omit important problem areas, papers on the following subjects were considered to be within the scope of the Specialist's Meeting: Analysis of existing post-accident instrumentation (in terms of range, qualification and redundancy) to support post-accident management. Requirements for post accident instrumentation and equipment - operating experience, regulations, standards; experience in upgrading of the existing instrumentation; instrumentation and equipment for emergency management systems (emergency rooms and national centers); post-accident computerized aids to assist operators; post-accident operating procedures; R and D in post-accident instrumentation, future trends. The present volume contains: (1) the papers presented by national delegates; (2) programme of the meeting; (3) description of the RIAR research facilities; and (4) list of participants. Refs, figs and tabs

[en] After the TMI accident, Post-accident Monitoring (PAM) Instrumentation based on the U.S. Guideline (R.G.1.97) was applied to Japanese PWRs. And we have back-fitted the PAM Instrumentation to old plants step by step. Recently, new type transmitters arrive on the market. They have better accuracy, and stability than old type. However, they cannot be applied as the PAM instrumentation, because new type are insufficient in a qualification for the PAM instrumentation and a modification to endure in-containment accident conditions. Hence, Japanese PWR utilities and Mitsubishi Heavy Industries are developing a new type transmitter for PAM instrumentation to improve accuracy and stability in the period of 1994 through 1996. This paper describes nowadays results in this development of a new PAM transmitter. (author). 8 figs, 3 tabs

[en] Historical reference, experimental base of the Institute, basic trends of the Institute activities such as: physical and technical issues of nuclear reactors and safety aspects incorporate; production of radionuclides and radionuclide products; nuclear fuel cycle; technical issues of ecologically safe technologies are described

[en] Identification of the types of accidents and proper actions is required at an early stage of an accident in nuclear power plants. The accident of the plant can be identified by their symptom patterns related to the principal variables and operating status of major equipment. The patterns are identified by the Self-Organizing Feature Map (SOFM), unsupervised artificial neural network, for feature mapping algorithm and the Hidden Markov Model (HMM), a stochastic technique for solving the time series problem. The off-line data from a compact nuclear simulator are vector quantized by SOFM clustering algorithm. The HMM is created for each accident from a set of training data which are the result of vector quantization. The accident identification is decided by calculating which model has the highest probability for given test data. The system uses a left-to-right model including 6 states and 16 input variables to identify 7 types of accidents and the normal state. The HMM is trained by the maximum-likelihood estimation method which uses forward-backward algorithm and Baum-Welch re-estimation algorithm. The optimal path for each model at the given observation is found by Viterbi algorithm, and then the probability of optimal path is calculated. The simulation results show that the proposed system identifies the accident types correctly. It is also shown that the diagnosis is performed well for incomplete input observation caused by sensor fault or malfunction of certain equipment. (author). 13 refs, 4 figs, 2 tabs

[en] A ventilation stack of WWER 440 NPP is serving to both of two reactor units constructed as twins. The air flow through the stack is approximately 162 m³s^-1 (5.10⁹ m³/yr) affected by the reactors operation mode (nominal power or refuelling). The hermetic zone (enclosure of the primary system components) at an accident is not vented directly to the stack due to automatic changes in the ventilation system airflows. Hence no uncontrolled radioactive matter should appear in the stack. Nevertheless some scenarios have been considered when this may happen (e.g. fuel damage at transport operations, leakages to vented areas at accidents). Standard gaseous effluent monitoring system RKS 2-03 provides the monitoring of the noble gases up to 2,2.10⁹ Bqm^-3. For the monitoring at accident conditions this may be inadequate. A typical value for a range of monitoring the radioactive matter in the air of common ventilation stack is 5.10⁴ - 5.10¹³ Bqm^-3. The purpose of the monitoring is to detect and evaluate significant releases and to enable the long-term monitoring after an accident. Other typical values suggested for monitoring noble gases in a ventilation stack are: up to 10¹² Bqm^-3 at air flow of 200000 m³h^-1; up to 10¹³ Bqm^-3 at air flow of 20000 m³h^-1. 5 refs, 5 figs

[en] The paper presents main topics and problems which arise during creating of regulatory requirements for post accident situations at NPP

[en] The requirements to computer-aided system of accidents analysis, based on symptom-oriented approach to initial events are given in this paper. The purpose, composition and realization of regression analysis algorithms of fast process measurements results under the Minor statistics Conditions are described. The description of information compacting methods for its long storing, on the base of adaptive digitization methods is given. The results of simulation on the base of computers elaborated technical means and applied software are described. (author). 4 refs, 3 figs, 3 tabs

[en] Emergency Response Centre (ERC) of Czech Republic is a highly specialized institution belonging to Nuclear Safety State Administration (SONS), which assures its activities both organizationally and technically. Main function of the ERC in the case of nuclear emergency is to fulfil the needs of SONS, Governmental Committee for Nuclear Emergencies in ER (GCNE ER) and the regional organs of State Authorities concerning the emergency planning and preparedness, evaluation of nuclear emergency consequences, including the emergency management and response. In the case of major failure or accident on NPP, the ERC carries out the performance analysis and review of a given NPP. It also monitors the dosimetric situation and transfers the recommendation to GCNE ER, Regional Emergency Management Committees and to NPP